It is a common practice in the art that a wafer having a certain device function is bonded to glass through a resin layer to form a wafer/glass laminate. For example, one well-known structure is completed by applying a photosensitive resin material to a silicon wafer having an optical sensor function, processing the material by lithography to form a resin layer around the sensor, and bonding the wafer to glass through the resin layer.
The formation of the adhesive layer by the photolithography process starts with the step of coating a photosensitive adhesive composition or disposing a photosensitive adhesive film on a silicon substrate (or glass substrate) to form a photosensitive adhesive layer. Then the photosensitive adhesive layer is exposed, baked and developed. A protective glass substrate (or silicon substrate) is placed in close contact with the adhesive layer. Heat and pressure are applied to establish a bond between the adhesive layer and the protective glass. This is followed by heat curing and dicing, obtaining a cavity structure package. The known photosensitive resin compositions include a photosensitive resin composition comprising an acrylic resin, a photo-polymerizable compound and a photo-polymerization initiator (Patent Document 1), and a photosensitive resin composition comprising a photosensitive modified epoxy resin, a photo-polymerization initiator, a diluent solvent, and a thermosetting compound (Patent Document 2).
Since the resin layer for bonding must be processed by lithography prior to use, the aforementioned wafer/glass laminate has several problems that cumbersome steps are involved, and a high pressure is necessary for bonding of glass.
To solve these problems, Patent Document 3 proposes a thermosetting resin through which a wafer is directly bonded to glass. As compared with the system including a cavity structure by the photolithography method, the method of Patent Document 3 has advantages including simple steps and a wide margin of bonding process. The method, however, is restricted in that the bonding resin in contact with a wafer having a device function should not be absorptive at wavelength in an overall spectrum of light transmitted by glass, or if absorptive, the resin should not be degraded by the absorption.